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Nitrate is a
polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalently bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. Unlike a molecule, which has a ...
with the
chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parent ...
.
Salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of cations and anions. Salts are composed of related numbers of cations (positively charged ions) and anions (negatively charged ions) so that the product is electrically ...
containing this
ion An ion () is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convent ...
are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are
soluble Solubility is the property of a solid, liquid or gaseous chemical substance called ''solute'' to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the ...
in
water Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent). It is vita ...
. An example of an insoluble nitrate is
Bismuth oxynitrate Bismuth oxynitrate is the name applied to a number of compounds that contain Bi3+, nitrate ions and oxide ions and which can be considered as compounds formed from Bi2O3, N2O5 and H2O. Other names for bismuth oxynitrate include bismuth subnitrate ...
.


Structure

The ion is the
conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton (H+) to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...
of
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of ...
, consisting of one central
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about t ...
atom An atom is the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so sma ...

atom
surrounded by three identically bonded oxygen atoms in a
trigonal planar left, 200px, Structure of boron trifluoride, an example of a molecule with trigonal planar geometry. In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, ca ...
arrangement. The nitrate ion carries a
formal charge and the nitrate anion In chemistry, a formal charge (FC) is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity. When determining th ...
of −1. This charge results from a combination formal charge in which each of the three oxygens carries a − charge, whereas the nitrogen carries a +1 charge, all these adding up to formal charge of the polyatomic nitrate ion. This arrangement is commonly used as an example of
resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of a periodically applied force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillati ...
. Like the
isoelectronic Isoelectronicity is an effect observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electron configurations, but differ by what specific elements are at certain locations in the struct ...
carbonate In chemistry, a carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula of . The name may also refer to a carbonate ester, an organic compound containing the carbonate g ...
ion, the nitrate ion can be represented by resonance structures:
400px, Canonical resonance structures for the nitrate ion


Dietary nitrates

A rich source of inorganic nitrate in the human diets come from leafy green foods, such as
spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either fres ...
and
arugula Rocket or arugula (American English) (''Eruca vesicaria''; syns. ''Eruca sativa'' Mill., ''E. vesicaria'' subsp. ''sativa'' (Miller) Thell., ''Brassica eruca'' L.) is an edible annual plant in the family Brassicaceae used as a leaf vegetable for i ...
. (inorganic nitrate) is the viable active component within
beetroot The beetroot is the taproot portion of a beet plant, usually known in Canada and the USA as beets while the vegetable is referred to as beetroot in British English, and also known as the table beet, garden beet, red beet, dinner beet or golden ...
juice and other vegetables. Drinking water is also a dietary source. Dietary nitrate supplementation delivers positive results when testing endurance exercise performance. Ingestion of large doses of nitrate either in the form of pure
sodium nitrate Sodium nitrate is the chemical compound with the formula . This alkali metal nitrate salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordinary saltpeter, potassium nitrate. ...
or beetroot juice in young healthy individuals rapidly increases plasma nitrate concentration about 2-3 fold, and this elevated nitrate concentration can be maintained for at least 2 weeks. Increased plasma nitrate stimulates the production of nitric oxide. Nitric oxide is important physiological signalling molecule that is used in, among other things, regulation of muscle blood flow and mitochondrial respiration.


Cured meats

Nitrite consumption is primarily determined by the amount of processed meats eaten, and the concentration of nitrates in these meats. Although nitrites are the nitrogen compound chiefly used in meat curing, nitrates are used as well. Nitrates lead to the formation of
nitrosamine Nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds of the chemical structure R2N−N=O, where R is usually an alkyl group. They feature a nitroso group (NO+) bonded to a deprotonated amine. Most nitrosamines are carcinogenic ...
s. The production of carcinogenic nitrosamines may be inhibited by the use of the antioxidants
vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy. Vitamin C is an essential nutrient involved in the repair of tissue and the en ...
and the
alpha-tocopherol#REDIRECT Alpha-Tocopherol {{R from other capitalisation ...
form of
vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitamin ...
during curing. Anti-hypertensive diets, such as the
DASH diet The DASH diet (Dietary Approaches to Stop Hypertension) is a dietary pattern promoted by the U.S.-based National Heart, Lung, and Blood Institute (part of the National Institutes of Health (NIH), an agency of the United States Department of Health ...
, typically contain high levels of nitrates, which are first reduced to
nitrite The nitrite ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. Nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite can also re ...

nitrite
in the saliva, as detected in
saliva testing Saliva testing or Salivaomics is a diagnostic technique that involves laboratory analysis of saliva to identify markers of endocrine, immunologic, inflammatory, infectious, and other types of conditions. Saliva is a useful biological fluid for ass ...
, prior to forming
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical, i.e., it has an unpaired electron, which is sometimes denoted by a dot in it ...
.


Occurrence and production

Nitrate salts are found naturally on earth as large deposits, particularly of
nitratine Nitratine or nitratite, also known as cubic niter (UK: nitre), soda niter or Chile saltpeter (UK: Chile saltpetre), is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Chemically it is the sodium analogue of saltpeter. Nitratine cr ...
, a major source of sodium nitrate. Nitrates are produced by a number of species of
nitrifying bacteriaNitrifying bacteria are chemolithotrophic organisms that include species of the genera e.g. ''Nitrosomonas'', ''Nitrosococcus'', ''Nitrobacter'', ''Nitrospina'', ''Nitrospira'' and ''Nitrococcus''. These bacteria get their energy by the oxidation of ...
in the natural environment using ammonia or urea as a source of nitrogen. Nitrate compounds for
gunpowder Gunpowder, also known as the retronym black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur (S), carbon (C), and potassium nitrate (saltpeter, KNO3). The sulfur a ...
were historically produced, in the absence of mineral nitrate sources, by means of various
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food prod ...
processes using urine and dung. Lightning strikes in earth's nitrogen-oxygen rich atmosphere produce a mixture of oxides of nitrogen which form nitrous ions and nitrate ions which are washed from the atmosphere by rain or in occult deposition. Nitrates are produced industrially from
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of ...
.


Uses

Nitrates are mainly produced for use as
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from li ...
s in
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peo ...
because of their high solubility and biodegradability. The main nitrate fertilizers are
ammonium The ammonium cation is a positively charged polyatomic ion with the chemical formula . It is formed by the protonation of ammonia (NH3). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary ammoni ...
,
sodium Sodium is a chemical element with the symbol Na (from Latin "natrium") and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotop ...
,
potassium Potassium is a chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmospheric ...

potassium
,
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to i ...
, and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column (group 2, or alkaline earth metals) of the per ...
salts. Several million kilograms are produced annually for this purpose. The second major application of nitrates is as oxidizing agents, most notably in explosives where the rapid oxidation of carbon compounds liberates large volumes of gases (see
gunpowder Gunpowder, also known as the retronym black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur (S), carbon (C), and potassium nitrate (saltpeter, KNO3). The sulfur a ...
for an example). Sodium nitrate is used to remove air bubbles from molten glass and some ceramics. Mixtures of the molten salt are used to harden some metals.


Detection

Almost all methods for detection of nitrate rely on its conversion to nitrite followed by nitrite-specific tests. The reduction of nitrate to nitrite is effected by copper-cadmium material. The sample is introduced with a flow injection analyzer, and the resulting nitrite-containing effluent is then combined with a reagent for colorimetric or electrochemical detection. The most popular of these assays is the Griess test, whereby nitrite is converted to a deeply colored
azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl. They are a commercially important family of azo compounds, i.e. compounds containing the linkage C-N=N-C. Azo dyes are widely u ...
, suited for UV-vis spectroscopic analysis. The method exploits the reactivity of nitrous acid derived from acidification of nitrite. Nitrous acid selectively reacts with aromatic amines to give diazonium salts, which in turn couple with a second reagent to give the azo dye. The
detection limit In analytical chemistry, the detection limit, lower limit of detection, or LOD (limit of detection), often mistakenly confused with the analytical sensitivity, is the lowest quantity of a substance that can be distinguished from the absence of th ...
is 0.02 to 2 μM. Methods have been highly adapted to biological samples.


Safety

The acute toxicity of nitrate is low. "Substantial disagreement" exists about the long-term risks of nitrate exposure. The two areas of possible concern are that (i) nitrate could be a precursor to nitrite in the lower gut, and nitrite is a precursor to nitrosamines, which are implicated in carcinogenesis, and (ii) nitrate is implicated in
methemoglobinemia Methemoglobinemia is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis). Complications may include seizures and heart ...
, a disorder of red blood cells hemoglobin.


Methemoglobinemia

Nitrates do not affect infants and pregnant women. Blue baby syndrome is caused by a number of other factors such as gastric upset, such as diarrheal infection, protein intolerance, heavy metal toxicity etc., with nitrates playing a minor role.


Drinking water standards

Through the Safe Drinking Water Act, the United States Environmental Protection Agency has set a maximum contaminant level of 10 mg/L or 10 ppm of nitrates in drinking water. An acceptable daily intake (ADI) for nitrate ions was established in the range of 0–3.7 mg (kg body weight)−1 day−1 by the Joint FAO/WHO Expert Committee on Food additives (JEFCA).


Aquatic toxicity

In
freshwater Fresh water (or freshwater) is any naturally occurring water except seawater and brackish water. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term specifical ...
or
estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
systems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia, levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species. Nitrate toxicity remains the subject of debate. In most cases of excess nitrate concentrations in aquatic systems, the primary sources are wastewater discharges, as well as
surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the so ...
from agricultural or
landscape A landscape is the visible features of an area of land, its landforms, and how they integrate with natural or man-made features.''New Oxford American Dictionary''. A landscape includes the physical elements of geophysically defined landforms su ...

landscape
d areas that have received excess nitrate fertilizer. The resulting
eutrophication Eutrophication (from Greek ''eutrophos'', "well-nourished") is a limnological term for the process by which a body of water becomes progressively enriched with minerals and nutrients. Water bodies with very low nutrient levels are termed oligot ...
and algae blooms result in anoxia and dead zones. As a consequence, as nitrate forms a component of
total dissolved solids Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular (colloidal sol) suspended form. TDS concentrations are often reported i ...
, they are widely used as an indicator of
water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through treatm ...
.


Domestic animal feed

Symptoms of nitrate poisoning in domestic animals include increased heart rate and respiration; in advanced cases blood and tissue may turn a blue or brown color. Feed can be tested for nitrate; treatment consists of supplementing or substituting existing supplies with lower nitrate material. Safe levels of nitrate for various types of livestock are as follows: The values above are on a dry (moisture-free) basis.


Salts and covalent derivatives

Nitrate formation with elements of the periodic table.


See also

*
Ammonium The ammonium cation is a positively charged polyatomic ion with the chemical formula . It is formed by the protonation of ammonia (NH3). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary ammoni ...
* *
Nitrification ''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring in separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of ammonia to ...
*
Nitratine Nitratine or nitratite, also known as cubic niter (UK: nitre), soda niter or Chile saltpeter (UK: Chile saltpetre), is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Chemically it is the sodium analogue of saltpeter. Nitratine cr ...
*
Nitrite The nitrite ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. Nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite can also re ...

Nitrite
, the anion *
Nitrogen trioxide Nitrogen trioxide or nitrate radical is an oxide of nitrogen with formula , consisting of three oxygen atoms covalently bound to a nitrogen atom. This highly unstable blue compound has not been isolated in pure form, but can be generated and obser ...
, the neutral radical *
PeroxynitratePeroxynitrate (or peroxonitrate) refers to salts of the unstable peroxynitric acid, HNO4. However, no solid salts are known. Peroxynitrate is unstable and decomposes to nitrate and dioxygen. See also * Sodium peroxynitrate References ...
, *
Sodium nitrate Sodium nitrate is the chemical compound with the formula . This alkali metal nitrate salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordinary saltpeter, potassium nitrate. ...


References


External links


ATSDR - Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity
{{Authority control Curing agents Functional groups
Garde manger{{cat main Food and drink preparation Cold Restaurants ...
Nitrogen cycle Non-coordinating anions Oxyanions Water quality indicators